A common metal casting process involves pouring liquid metal through a spout and into a mold where the molten metal solidifies to form a billet or slab. The flow of metal through the spout is often controlled by a control pin that is located within the spout. The control pin can be raised in order to increase the rate of flow of metal through the spout, or lowered to decrease or interrupt the flow of metal.
In order to prevent some of the molten metal from solidifying before exiting the spout, the control pin must have a temperature near that of the molten metal. In practice, this means that the control pin must be pre-heated prior to operation. In most cases, this involves heating the control pin in a furnace and, once it attains the desired temperature, manually transferring it to the spout. This process adds a considerable amount of complexity to the casting process, and also gives rise to the risk of a serious accident when transferring the hot control pin from the furnace to the spout.
To avoid such additional complexities and risks in the casting process, a control pin which can be pre-heated in situ is preferred. Known to the applicant is the International Patent Application WO 2011/043759 (COOPER et al.). Cooper discloses a heated control pin comprising an inner cavity, and a heater element placed therein. This design has room for improvement; a configuration allowing the pin to be heated faster and requiring less energy is preferred.
In order to withstand physical wear and the high temperatures of the casting process, control pins are often manufactured using multiple refractory materials. For example, in U.S. Pat. No. 7,165,757, the body of the control pin is made of a laminated composite ceramic material, and the tip of the control pin is made of a different wear-resistant ceramic material. Other pin designs may also use multiple layers of different materials. This can be complex to manufacture, and may also be subject to degradation due to the materials having different thermal expansion coefficients. A control pin which is simple to manufacture and durable is preferred.
It is therefore an object of the present invention to provide a control pin which alleviates at least some of the above-mentioned issues.